SOIL BIOLOGICAL-ACTIVITY IN RECENT CLEARCUTS IN WEST-CENTRAL ALBERTA

Soil biota response to changes in the soil physical environment follow ing forest harvesting is relatively unknown in boreal forests. Soil bi ological activity was measured at four sites with Luvisolic soil follo wing clear-cut forest harvesting. Aerobic respiration rate and cellulo se decomposition in flooded soils were measured on soil samples collec ted from treatment plots subjected to tree removal only and tree remov al associated with three levels of skidding activity immediately after clear-cut harvesting and after 1 and 2 yr. More than half of variatio n in respiration and cellulose decomposition rates was related to soil properties. Soil respiration rate increased significantly after 1 yr but was not affected by skidder traffic. Cellulose decomposition was h ighest in soil with air-filled porosity <0.10 m(3) m(-3), and increase d significantly with skidder traffic. Air-filled porosity measured in the field at the time of harvest indicated a poorly aerated environmen t that becomes wetter in subsequent years. The results imply that soil had biota well adapted to poor soil aeration. The development of a fu lly anaerobic soil environment following forest harvesting only occurr ed on compacted soil after heavy precipitation, but partial anaerobios is of these boreal forest soils was common. Although partial anaerobio sis increased decomposition rate, it is considered sufficient to adver sely affect the growth of plant roots and change the availability and mobility of nutrients.